This invention relates to instruments for use in endoscopic surgery. More particularly, this invention relates to instruments with a disposable auto-regulating heater for use in endoscopic surgery.
Minimally invasive surgery such as endoscopic surgery allows for major surgical operations to be performed with reduced pain and disability relative to conventional "open" surgery. In performing endoscopic surgery, the surgeon does not cut a large incision through the body wall to obtain access to the tissue requiring treatment. Instead, an endoscope, typically a miniaturized video camera, and certain specially-designed surgical instruments are inserted through a trocar tube or similar device. Trocar tubes, typically having a 5 mm to 10 mm inside diameter, produce only a small opening. The image provided by the endoscope is displayed on a large video screen or other type of monitor, thereby affording the surgeon enhanced visual control of the specially-designed instruments.
Endoscopic surgery is possible whenever a small optical instrument (endoscope) and miniaturized operating instruments can be inserted into the body cavity or other anatomical space. Such miniaturized operating instruments have been developed for endoscopic surgery in the abdomen ("laparoscopy"), in the chest ("thoracoscopy") and in joints ("arthroscopy").
In performing both "open" and endoscopic surgical procedures, the surgeon must control bleeding that occurs when tissues are incised. Such bleeding obscures the surgeon's vision, reduces precision, and often necessitates slow and elaborate procedures to perform the surgery.
Controlling flow of blood from incised tissue is readily accomplished in "open" surgical procedures, because the surgeon can directly touch and manipulate the various tissues. Bleeding from incised tissue is controlled by blotting or evacuating the accumulating blood. This step of removing the blood permits visual observation of the vessels for clamping or tying of those vessels to inhibit further blood loss.
In performing endoscopic surgery, the surgeon forgoes direct manual access to the tissue being operated upon. Thus, traditional means of physically controlling bleeding (i.e., clamping and tying) are unavailable. Other techniques must then be employed to control bleeding during the surgical procedure. One such technique, which was first employed in "open" surgical procedures, is to thermally heat the bleeding tissue. Such thermal heating reduces the tendency of severed tissue to bleed.
For "open surgery" it is known to provide surgical scalpels which employ a blade with an adjacent resistive heating element. The resistive heating element provides thermally-enhanced cutting, in addition to hemostasis, when electrical current is passed through the element. Although such resistive elements can be readily brought to a suitably high and constant temperature in air prior to contacting tissue, they rapidly cool when brought into contact with tissue. During "open" surgery, non-predictable and continually varying portions of the blade contact the tissue as it is being cut. As the blade cools, its ability to cut tissue and provide hemostasis becomes markedly less effective. Furthermore, tissue tends to adhere to the blade. If additional power is applied by conventional means to counteract this cooling, the additional power may be delivered to the uncooled portions of the blade, thus resulting in tissue damage and blade destruction.
Shaw U.S. Pat. No. 4,185,632 shows an improved surgical cutting instrument in which the temperature of the cutting portion of the blade is self-regulating. Radio frequency electrical currents maintain the temperature within an elevated preselected temperature range. These currents flow within variable skin depths in an electrical conductor disposed near the cutting edge of the blade. This variable skin depth effect produces self-regulation of the blade temperature.
In addition to the ability to provide hemostasis, and to remotely cut and dissect tissue, endoscopic surgery requires the use of instruments that reduce adherence of tissue to the instrument. Coagulum buildup and sticking limits the usefulness of the instrument and may cause undesirable tissue damage and bleeding. Also, the adherence of tissue to such surgical instruments limits the surgeon's control of the instrument.
It would therefore be desirable to provide a low cost hemostatic instrument for endoscopic surgery which has the ability to precisely control the location and quantity of thermal energy which is delivered to tissue.
It would also be desirable to provide an endoscopic instrument that has the ability to provide localized and precise thermally-enhanced cutting of tissue.
It would further be desirable to provide an endoscopic instrument which reduces the adherence of tissue and coagulum to the instrument so as to reduce tissue damage associated with such adherence and to maintain good thermal power delivery between the heating means and the tissue by reducing the thermal impedance associated with tissue or coagulum build up on said heating means.
In addition to the above, it would still further be desirable to provide an endoscopic instrument that is capable of being used for a wide variety of endoscopic surgical procedures. Thus, it would also desirable to provide an endoscopic instrument that has a reusable universal handle which is capable of accommodating a wide variety of disposable working surfaces wherein a used working surface can be easily removed from the handle and replaced with a new or differently shaped working surface.